Light pickup unit



Sept. 11; 1956 R, FALGE ET AL LIGHT PICKUP UNIT 3 Sheets-Sheet 2 FiledNov. 10 1951 INVENTORS. 7M! /2 $7:

(VI/Zia v I I v 1/ f I ATTOR/VEXX- Sept. 11, 1956 R. N. FALGE ETAL2,762,932

LIGHT PICKUP UNIT Filed NOV. 10, 1951 3 Sheets-Sheet I5 United StatesPatent LIGHT PICKUP UNIT Robert N. Falge, George W. Onksen, Jr., HaroldE. Todd, and Charles W. Miller, Anderson, Ind., assignors to GeneralMotors Corporation, Detroit, Mich., a corporation of DelawareApplication November 10, 1951, Serial No. 255,764

'15 Claims. (Cl. 250-226) The present invention relates to lightsensitive devices and more particularly to an improved light pickup unitfor a light actuated control system such as an automatic headlightdimmer for automotive vehicles.

Light actuated automatic headlight dimmers have been proposed for someyears now; however, because of certain 'difliculties in their operationthey have been unsatisfactory and therefore have failed to gain anypopularity. Perhaps the greatest defect in these automatic headlampdimmers is their failure to provide a high sensitivity, which isselective to light originating from the headlamps of oncomingautomobiles. In those devices which utilize a highly sensitive systemthe dimmer becomes subject to actuation by light sources other thanthose of oncoming vehicles. The proper operation of such a dimmer deviceis, for example, precluded during the twilight hours since light fromthe sky has sufficient intensity to actuate the circuit. On the otherhand, if a less sensitive system is used, actuation of the dimmer occursonly after the oncoming vehicle is quite close, thus resulting in aswitching from high to low beam lights which is too late to accomplishthe purpose for which the dimmer was intended.

Another difficulty with the automatic headlamp dimmers which have beenproposed in the past is their failure to provide adequate means forgathering light only from within a predetermined angle of approach andalso to provide adequate means for uniformly utilizing the gatheredlight for causing dimmer actuation irrespective of its angle ofapproach. In prior devices there has been far less sensitivity to lightapproaching the pickup unit at an angle than to that which approachesfrom directly ahead. This characteristic i advantageous to the extentthat it prevents actuation of the dimmer circuit by street and otherlights which are displaced far to the left or right of the vehicle.However, within a certain predetermined relatively small angle it isvery desirable to have uniformity of sensitivity to light irrespectiveof its direction of approach from within that angle. Such a uniformityis advantageous because headlamp dimming results at about the samedistance regardless of whether the approaching vehicle is slightlydisplaced to the left or right or up or down, as would be the case, forexample, if the vehicle were rounding a curve or coming over the top ofa hill.

Accordingly, it is an object of this invention to provide a light pickupunit for light actuated control systems which has highly increasedsensitivity to predetermined types of light. Another object of thisinvention is the provision of a light pickup which is effective ingathering light only through a predetermined angle of light approach andat the same time is effective in uniformly utilizing the gathered lightfor control actuation. These objects are carried out in accordance withour invention by the provision of a light pickup unit having novel lightdirecting and filtering means for a photosensitive element and havingnovel positioning and supporting means. Other objects "and advantages ofthe invention will more fully 2,762,932 Patented Sept. 11, 1956 iceappear in the following description of the preferred embodiments shownin the accompanying drawings in which:

Figure l is a top view with parts broken away of the preferredembodiment of the invention.

Figure 2 is a cross-sectional view taken on the line 2-2 of Figure 1.

Figure 3 is a perspective view with parts broken away of the embodimentshown in Figures 1 and 2.

Figure 4 is a view of the pickup unit mounted on a vehicle.

Figure 5 is a perspective view of the preferred embodiment of the lightfiltering and directing element.

' Figure 6 is a perspective view with parts broken away of anotherembodiment of the invention.

Figure 7 is a diagrammatic and graphic representation of the verticaloptics of the preferred embodiment of the light pickup unit.

Figure 8 is a diagrammatic and graphic representation of the horizontaloptics of the preferred embodiment of the light pickup unit.

Referring now to the drawings, Figures 1, 2 and 3 represent thepreferred modification of our invention which includes an opaque housing10 made of some suitable material such as plastic or metal. The housingis pro vided with a light transmitting opening 12 covered by a lightcondensing lens 14. In the embodiment shown the lens 14 has a steppedstructure as indicated generally at 15 so as to attain substantiallyuniform lens thickness; however, any suitable condensing lens structurewill sufiice. A photosensitive element 16 is mounted in the housing 10by a support such as bracket 18 which is connected to the housing by ascrew member 20. The photosensitive element is mounted so that it facesthe light opening, that is, the element is positioned so that itscathode, which is the light sensitive portion of the tube, faces theopening 12.

In the particular embodiment shown the housing comprises a bottomsection 22 and a top section 24 maintained in assembled relationship bythe overlapping edge joint 26 and by the bolts 28 which pass through thebottom wall of the bottom section 22 and threadedly engage threadedbores provided in the projection 30 which are integral with the top wallof the top housing section 24. Such a sectionally constructed housingfacilitates maintenance by allowing easy access to the various enclosedelements.

The electrical contacts 32 of the photosensitive element 16 are providedwith suitable electrical connections illustrated at 34 so as to maintainthem in electrical contact with the wires 36 which are a part of thecontrol circuit. It is understood that the electrical connections willbe arranged to suit the type of photosensitive element used. In thepreferred embodiment the wires 36 are connected to the electricalcontacts 32 by brazing or soldering the ends of the wires directly tothe contacts. Such a means is helpful in preventing the loosening of theelectrical connection due to vibration; however, a socket member of theconventional type used with such elements will serve to establish theelectrical connection.

It will be noted that the connection 34 is protected from any pullingforce exerted on the wires external of the housing by providing anenlargement such as knot 38 adjacent the wire exit opening 40 in thehousing 10.

In the preferred embodiment of our invention the support for the housingcomprises the structure shown by Figure 2 wherein the housing 10 ishinged at 42 to the the bottom of the housing 10. A smaller bore 58 isprovided in the support 44 and is threaded for the reception of theadjusting screw 60, the bottom of which is slotted in the usual mannerfor turning by a screwdriver, and the top of which abuts the bottomportion 62 of the housing. It will be seen that the spring 50 tends torotate the housing vertically and thereby urges and maintains the bottomportion 62 of the housing against the top of the adjusting screw 60.Thus, by turning the adjusting screw 60, thereby changing its verticalposition, the vertical angle of the housing can be adjusted withinlimits as desired. The hollow center of the spring 50 provides aconvenient exit passage for the wires 36 which, as mentioned previously,connect the photosensitive element with the electrical control circuit.

Such a support is extremely useful since it allows vertical aiming ofthe light pickup unit. The provision of this vertical aiming meansallows for the positioning of the unit in various locations on thevehicle with a retention of the highest sensitivity possible for thepick up of light from the desired vertical angle. We have found it bestto mount the pickup unit, as is shown in Figure 4, inside the vehicle onthe left side and immediately behind the windshield 63 and positioned sothat the light opening 12 in the housing 10 faces the windshield 63 forthe reception of light passing therethrough. The unit may convenientlybe mounted by means of the adjustable support 44 to the top of theinstrument panel 65 as shown in Figure 4. Such an inside mounting hasseveral advantages: since the windshield is cleaned frequently, the unitis less troubled with light obstruction from dirt; being inside, theunit is protected from weather; being mounted on the left, the unit cansee around a vehicle ahead to dim for an approaching vehicle and, beingmounted high, the unit can see approaching headlamps over a rise in theroad at about the same time as the driver. Also, the high mountingpermits the effective light angle to be as low as possible without beingaffected by the back re fiections from the vehicles own headlamps. A loweffective light angle permits larger vehicle loading and aimingtolerances.

Separating the photosensitive element 16 from the opening 12 is apartition or wall 64 provided with an aperture 66 which is in line withthe opening 12 and the light receiving portion of the photosensitiveelement 16. In the embodiment shown, the wall 64 consists of an uppersection 68 and a lower section 70, upper section 68 being integral withthe top section 24 of the housing and lower section 70 being integralwith the bottom section 22 of the housing. Thus, the wall 64 which isformed from the abutting upper and lower sections is effective inblocking the light rays from the opening 12 except for those which aretransmitted through the aperture 66.

Covering the aperture 66 is the light refracting member 72 which willhereinafter be discussed in detail. The member 72 is maintained inposition by the plate 74 which is secured to the wall 64 by the plateretaining screw 76. The plate 74 has a slot 78 which gives it aU-shaped, the slot being necessary of course to allow the transmissionof light through the member 72. As can best be seen in Figure 3, thelight refracting member 72 is held from lateral and vertical movement bythe shoulders 80 and the raised portion 81 which are integral with thelower section 70 of the wall 64. Upward movement of the member 72 can beprevented by merely tightening the screw 76 until there is sufficientfrictional force exerted by the plate 74 to prevent such movement.

In one embodiment of our invention the member 72 consists of a lightfiltering element, which is effective in allowing the passage only oflight of a selected color. Such a light filter is particularlyadvantageous when the photosensitive element used is an electronmultiplier type photoelectric tube. This type of tube, which We use inthe preferred embodiment of our invention, is hundreds sensitiveelements and thus allows for an extremely sensitive control systemwithout the use of considerable amplification equipment in the circuit.However, such a tube is extremely sensitive to blue light. Thus, whenused on automatic headlamp dimmers it is subject to actuation during thetwilight hours by skylight and, during the nighttime hours, bymoonlight. When, however, the electron multiplier tube is used incombination with the filtering element of this invention, the pickupunit retains a high sensitivity to artificial light such as that fromvehicle headlamps, but remains relatively insensitive to sky andmoonlight. We have found that an amber-colored filter is particularlyeffective for blocking blue light and for transmitting the light fromvehicle headlamps. However, any suitably colored filter can of course beused within the scope of our invention.

In the preferred embodiment of our invention as shown by Figures 1, 2and 3, member 72 is shaped so as to give it certain light refractingproperties. A shape which we have found particularly suitable to givethose infracting properties which are desirable and which will behereinafter discussed in detail, is shown in Figure 5. Referring toFigure 5, the generally rectangular body 84, which can be of anysuitable transparent material such as glass or Lucite plastic, isprovided with a double prism arrangement 86 on one face and acylindrical lens 88 on its oppositely disposed face. The longitudinalaxis of the cylindrical lens, it will be noted, is parallel with thelong dimension of the rectangular body 84 and is at right angles to theridge line 90 of the double prism arrangement. The dimensions of thedouble prism 86 on the one face and of the cylindrical lens 88 on theoppositely disposed face are not coextensive with the dimensions of therectangular body itself, thus providing horizontal flat surfaces 92 onthe cylindrical lens face and vertical flat surfaces 94 on the doubleprism face. As can best be seen in Figure 3, such dimensioning allowsthe cylindrical lens to fit snugly in the housing wall aperture 66 andthe double prism to fit snugly in the plate slot 78, the horizontal andvertical flat surfaces 92 and 94 respectively abutting the housing wall64 and plate 74. We prefer to mold or cut the entire member 72 from asingle integral piece of transparent material; however, it could ofcourse be made of separate parts bonded in some suitable manner.

Referring again to Figure 5, the cylindrical lens face which is the rearface as mounted in the assembly, has a discontinuous covering of someopaque material such as the black paint coating 96 or cardboard, or thelike. The discontinuous covering provides a light transmitting window98. It will be noted that the top as well as the bottom (not shown) ofthe member 72 are also coated or covered but the front or prismatic faceis left uncovered. Thus, when the light refracting member 72 isassembled in the unit as shown in Figures 1, 2 and 3, the window 98provides the only light opening for the transmission of light from thehousing opening 12 to the photosensitive element 16.

In our preferred embodiment the window 98 is positioned at the focalpoint of the lens 14 and is dimensioned so that a vertical spread angleof about 6 and a horizontal spread angle of about 12 are attained. Thehorizontal spread angle is uniformly distributed to the left and right;that is, the unit gathers light from about 6 to the left and about 6 tothe right. However, as regards the distribution of the 6 vertical spreadangle, we have found it advantageous if light dimming is caused only bythat light which has a direction of approach within a vertical angle ofabout 2 below and about 4 above a plane which passes through the centerof the lens and which is horizontal when the car is in a level position.This plane will hereinafter be referred to as the horizontal plane ofthe vehicle. This vertical spread angle of about 4 above and about 2below is accomof times more sensitive than the ordinary type photo- 75plished by positioning the pickup unit on the vehicle so that the centerof the window 98 -is slightly below the horizontal plane of the vehicle.Such positioning can of course be accomplished by means of the support44, heretofore described, which allows for vertical angular adjustment.

In Figure 4 we have illustrated the distribution of the 6 verticalspread angle as the pickup unit is mounted on the vehicle. It will benoted that the unit is vertically adjusted so that it gathers light fromwithin an angle of about 4 above and about 2 below the horizontal planeH of the vehicle.

By this proper positioning of the pickup unit so that the center of thewindow 98 is located below the horizontal plane of the vehicle to theextent necessary to attain a vertical actuating spread angle of about 4above and about 2 below the vehicle horizontal plane, a system isaccomplished which is highly sensitive to oncoming light but whichavoids actuation by road reflections of the lights of the vehicle onwhich it is mounted.

It is understood, of course, that while in our preferred embodiment thewindow 98 is of a height and width and is positioned so as to make theunit sensitive to light approaching within a Vertical angle of about 4up and about 2 down in respect to the horizontal plane of the vehicleand about 6 left and 6 right in respect to the focal axis of the lens,in some cases it may be desirable to use a window of different size toobtain different light gathering angles.

Since the size of the window determines the light approach angle throughwhich the unit will be effective in gathering light, it is useful to usea lens 14 which has been corrected for spherical aberration in order toattain a more clearly defined focal point or light focus. When such alens is used, rather than there being a gradual decrease in sensitivityas the angle between the direction of light approach and the lens axisbecomes greater, there will be approximately the same magnitude ofsensitivity until the approach angle becomes such that the well definedlight focal point reaches the edge of the window, at which time therewill be a sharp decrease. Thus, the use of a condensing lens correctedfor spherical aberration in combination with the window 98 aids ingiving a uniform sensitivity to light approaching from within apredetermined and well defined approach angle.

As was mentioned above, the member 72 is shaped so as to impart certainadvantageous light refracting properties. These light refractingproperties can best be discussed by reference to Figures 7 and 8 whichdiagrammatically and graphically illustrate the advantageous propertiesof our light refracting member 72. In Figure 7a which shows the verticaloptics of the member 72, the light 101 approaches the lens parallel withthe lens focal axis, that is, it approaches from some light source whichis directly in front of the light pickup unit. This light is focused bythe lens 14 toward the member 72 having the prismatic front face 86,later described with reference to Figure 8, and the cylindrical lensrear face 88 and, after passage through the member, falls across acathode area designated as A. We wish to point out that we do not heredescribe nor do we accurately show the precise and detailed refractionof the light by the member 72, but rather emphasize only the net effectof the refraction as regards the cathode area which is affected by thislight.

The light 102 approaches the lens 14 at some small vertical angle to thelens focal axis, that is, it approaches from some source which isupwardly displaced from the pickup unit. This light 102 is also focusedby the lens 14 toward the member 72 where it is refracted upwardly bythe cylindrical lens face 88 in such a way as to cause it to fall on thecathode area B. If the member 72 were not in the system this light wouldfall on some area below that indicated at B in such a way that some ofthe light would miss the cathode completely and the remainder wouldstrike the cathode at its bottom-most portion. Due, however, to the useof the member 72 with the cylindrical lens rear face 88, the area Bapproximates the area A and thus, by means of the cylindrical lens rearface, the cathode area affected by the light 102, which enters the unitfrom some direction at a vertical angle to the lens focal axis, isapproximately the same as the area affected by the light 101 enteringthe unit from a direction parallel with the lens focal axis. Since thesensitivity of the unit is dependent upon the cathode area impinged bythe light rays, and since sensitivity is increased by directing thelight so that it contacts the cathode closer to its center, it will beseen that the vertical optics resulting from the light refracting member72 are such as to impart to the unit a more uniform sensitivityirrespective of the vertical angle of approach of the gathered light.

The diagram illustrates the light rays entering from some source abovethe unit. The same uniformity of sensitivity will of course occur asregards light entering from some source below the unit except that, asdiscussed above, the lowest effective light rays are only about 2 belowthe horizontal plane of the vehicle, whereas light rays up to about 4above will effect actuation.

The graphs 7b and 70 more clearly illustrate the uniformity attainedthroughout the vertical actuation spread angle. In graphs 7b and 7cwhich show the results of tests conducted using a low intensity lightsource, the dimming distance in feet is plotted against the verticalangle of approach of the light, that is, the vertical angle between thehorizontal plane of the vehicle and the line which would indicate thedirection of approach of the light. On the graphs the vertical angle isdesignated as degrees U (up) and degrees D (down). Plot 70 shows therelationship between dimming distance and vertical angle of lightapproach for a unit not utilizing the light modifying member 72, andplot 7b shows the relationship for a unit employing the member 72. Itwill be noted from graph 70 that sensitivity decreases very rapidly withan increased vertical angle of light approach when the light refractingmember is not used. Thus, while the distance at which dimming will takeplace with the low intensity light from a test bulb is 24 feet, when thelight approaches parallel to the vehicle horizontal plane, the dimmingdistance decreases to about 15 feet when the light approaches from adirection 1 below and is down to about 8 feet when the light aproachesfrom 2 below. When the member 72 is placed in the system, however, a fargreater uniformity is attained. The dimming distance for lightapproaching parallel to the horizontal plane of the vehicle is about 24feet. At a 1 downward displacement the distance remains 24 feet, and ata 2 downward displacement falls only to about 18 feet. The graph 7b alsovery clearly illustrates the sharpness of the decrease in sensitivity at2 below and 4 above the horizontal plane of the vehicle. It will benoted that, while light entering from 2 below actuates the dimmer atabout 18 feet, light of the same intensity approaching from an anglevery slightly more than 2 below will cause no actuation whatsoeverirrespective of its distance from the unit. Thus, the unit utilizing thelight modifying member 72 gathers light only from within a well definedvertical angle and at the same time provides for uniformity of actuationby the gathered light irrespective of its direction of approach.

Figure 8a illustrates the horizontal optics of the light refractingmember 72. Light 108 approaching parallel to the lens focal axis isfocused by the lens 14 toward the member 72 and refracted by theprismatic face 86 on the member 72 so as to fall on cathode area C.Light 110 approaching at some small horizontal angle to the lens focalaxis is focused by the lens 14 and refracted by the prism toward thecenter of the cathode so as to fall on area D. Except for the presenceof the prismatic face 86, some of this light would miss the cathodeentirely and the remainder would strike only the edge portion of thecathode. With the member 72 in the system, however, the area affected bythe light 110 is close to the cathode 7 center and approximates the areaaffected by the light 108, thus attaining uniformity of sensitivityirrespective of the horizontal angle of approach of the light.

The graphs 8b and 8c illustrate the advantages of our improved opticalsystem insofar as the horizontal light gathering properties areconcerned. Graph 8c is plotted from results obtained in tests conductedwith a unit not employing the member 72, while graph 8b is plotted fromresults obtained in the same tests conducted with a unit employing themember 72. The graphs designate the horizontal angle of light approachas degrees L (left) and degrees R (right). Here again a low intensitytest light source was used for test purposes. It will be seen from graph8b that a sharp decrease in sensitivity is attained at 6 to the left and6 to the right, and that within these limits there is a greatimprovement in the uniformity of sensitivity attained irrespective ofthe horizontal light approach angle. The results shown in graph 8b arein sharp contrast to those illustrated in graph So which indicate agradual decrease in sensitivity as the horizontal approach angle becomesgreater.

While in our preferred embodiment we use a light modifying member havingone double prism face and one cylindrical lens face, we wish to pointout that our invention is not limited to this configuration. A doubleprismatic face on both sides of the member will, for example, giveresults comparable to those discussed above. Any member which causeslight entering the unit from an angle, vertical or horizontal, to bedirected toward that area of the photosensitive element which iscontacted by light entering the unit from directly ahead, thus resultingin uniformity of sensitivity, will of course suflice to serve thepurposes of the double prism-cylindrical lens faced member discussedabove and is therefore within the scope of our invention.

In our preferred embodiment the member 72 is made of some lightfiltering material such as amber-colored plastic. Thus the unit combinesthe advantages of light filtering and the advantages of light directingto attain uniformity of sensitivity for selected types of light by theutilization of a light filter having the refracting properties describedabove. It is of course within the scope of our invention to use separatemembers for light filtering and for light directing. It is possible, forexample, to use a light filtering condensing lens in combination with alight refracting member made of an uncolored material. In some instancesit is advantageous, depending upon the specific characteristics whichare desired in the pickup unit, to use the light directing means aloneso as to attain uniformity of sensitivity or to use the light filteringmeans alone to attain light selectivity.

Figure 6 shows an embodiment of our invention using filtering meansalone. The structure is the same as that shown in Figures 1, 2 and 3except that, in place of the light refracting member, a flat sidedfilter 116 made of some transparent colored material such asamber-colored glass or plastic is used. The flat sided filter 116 isheld in position to cover the aperture in the housing Wall 118 by theslotted plate 120 which is secured to the housing wall by the screw 122.In the embodiment shown the filter has a discontinuous opaque coating124 on one side so as to provide the window 126. However, a similarresult may of course be accomplished by the use of a plate which insteadof being slotted, is provided with an aperture at or near its center.

As was previously mentioned, the use of such a filter is particularlyadvantageous when an electron multiplier type photosensitive tube isused as the light sensitive element.

By means of our invention a light pickup unit for light actuated controlsystems which is highly sensitive to selected types of light whichgathers light only from within predetermined vertical and horizontalangles of light approach and which has increased uniformity ofsensitivity to the gathered light irrespective of its angle of approach,is accomplished. The provision of inside the vehicle mounting on theleft side and of vertical aiming means for the unit give additionaladvantageous features which contribute to the highly improved over-allefiiciency of automatic headlamp dimmer systems.

While we have described our invention with reference to particularembodiments thereof, it is not to be so limited since changes andalterations therein may be made which are within the full intended scopeof this invention as defined by the appended claims.

What we claim is:

1. A light gathering device for a photosensitive element comprising ahousing enclosing said photosensitive element and having an openingtherein and a light directing element in said housing, said lightdirecting element comprising a body of transparent material, said bodyhaving a cylindrical lens on one face thereof and a double prism on theoppositely disposed face thereof, a discontinuous opaque covering onsaid face having said cylindrical lens thereon, said discontinuouscovering providing a light transmitting window on the face of saidcylindrical lens.

2. A light directing and filtering device for a photosensitive elementcomprising a housing enclosing said photosensitive element and having anopening therein and a light filter element in said housing, said lightfilter element comprising a body of light filtering material, said bodyhaving a cylindrical lens on one face thereof and a double prism on theoppositely disposed face thereof, a discontinuous opaque covering onsaid face having said cylindrical lens thereon, said discontinuouscovering providing a light transmitting window on the face of saidcylindrical lens.

3. A light pickup unit for a light actuated control system comprising ahousing having an opening therein, a photosensitive element facing saidopening, a light con densing lens in said opening, a filter positionedat the focal point of said lens, said filter having a discontinuouscovering on one face thereof to provide a light transmitting window,said window limiting the light falling on said photosensitive element tothat entering said opening from within a vertical angle of about 3 tothe optical axis of said lens and from within a horizontal angle ofabout 6 to the optical axis of said lens.

4. A light pickup unit for a light actuated control system comprising ahousing having an opening therein, a photosensitive element in saidhousing facing said opening and a light refracting member between saidphotosensitive element and said opening, said light refracting memberhaving a double prism on one face thereof and a cylindrical lens on theoppositely disposed face thereof.

5. A light pickup unit for a light actuated control system comprising ahousing having an opening therein, a photosensitive element in saidhousing facing said opening, a light condensing lens in said opening, alight refracting member in said housing positioned at the focal point ofsaid lens for directing light from said opening to said photosensitiveelement, said member having oppositely disposed prismatic andcylindrical lens faces, and means for filtering the light directed tosaid photosensitive element.

6. A light pickup unit for a light actuated control system comprising ahousing having an opening therein, a photosensitive element in saidhousing, a light condensing lens in said opening, a wall in said housingbetween said opening and said photosensitive element, said wall havingan aperture therein, a filter element covering said aperture, a platehaving an opening therein for securing said filter 1n aperture coveringposition, means for securing said plate to said Wall, said filter havinga cylindrical lens on the rear face thereof fitting into said apertureand a double prism on the front face thereof fitting into said plateopening and a discontinuous opaque coating on said rear face, saiddiscontinuous coating providing a light transmitting window.

7, A light pickup unit for vehicle headlight dimming comprising ahousing having an opening therein, a photosensitive element in saidhousing facing said opening, a support for said housing, a hinged jointconnecting said support to said housing, said hinged joint allowingvertical rotation of said housing on said support through apredetermined angle, resilient means in said support urging verticalrotation of said housing on said support in one direction and avertically adjustable screw member on said support abutting said housingand limiting the extent of the rotation urged by said resilient member.

8. A light pickup unit for vehicle headlight dimming comprising ahousing having an opening therein, an electron multiplier typephotosensitive element in said housing facing said opening, saidphotosensitive element being blue sensitive, a lens in said opening, awall between said lens and said photosensitive element having an openingtherein at the focal point of said lens, a light refracting filter insaid aperture for blocking blue light from said photosensitive element,a discontinuous opaque covering on said filter providing a window forlimiting the light falling on said photosensitive element to thatapproaching said opening from within a predetermined angle, said filterhaving a double prism on one face thereof and a cylindrical lens on theoppositely disposed face thereof for substantially equalizing theactuating effect of the light falling on said photosensitive element, asupport for said housing and means on said support for aiming the pickupunit.

9. A light pickup unit for vehicle headlight dimming comprising ahousing having an opening therein, a photosensitive element in saidhousing facing said opening, a light blocking wall in said housinghaving an aperture therein, said aperture limiting the light falling onsaid photosensitive element from said opening to that approaching saidunit from Within a vertical angle of about 6 and from within ahorizontal angle of about 12, a support for mounting said pickup unit onthe vehicle, and means on said support for aiming the pickup unit sothat said vertical angle is positioned with 4 above and with 2 below aline passing through the center of said opening and parallel with thehorizontal axis of the vehicle.

10. A light pickup unit for a vehicle automatic headlight dimmer devicecomprising a housing having an opening therein, a photosensitive elementin said housing, a condensing lens in said opening, an opaque wall insaid housing between said photosensitive element and said lens having anaperture therein located at the focal plane of said lens, said aperturelimiting the light falling on said photosensitive element to thatapproaching said opening from within predetermined vertical andhorizontal angles, and optical means in said housing and adjacent saidaperture to substantially equalize the actuating effect on saidphotosensitive element of the light entering said opening irrespectiveof its angle of approach within said predetermined angles, and mountingmeans on said unit adapted to secure said unit to a vehicle.

11. A light pickup unit for a vehicle automatic headlight dimmer devicecomprising a housing having an opening therein, a photosensitive elementin said housing, a condensing lens in said opening, an opaque wall insaid housing between said photosensitive element and said lens having anaperture therein located at the focal plane of said lens, said aperturelimiting the light falling on said photosensitive element to thatapproaching said opening from within predetermined vertical andhorizontal angles, and optical means in said housing and adjacent saidaperture to substantially equalize the actuating efiect on saidphotosensitive element of the light entering said opening irrespectiveof its angle of approach within said predetermined angles, and anadjustable mounting means on said unit adapted to secure said unit to avehicle and to allow said unit to be aimed.

12. A light pickup unit for a vehicle automatic headlight dirnmer devicecomprising a housing having an opening therein, a photosensitive elementin said housing, a stepped spherical condensing lens corrected forspherical aberration in said opening, an opaque wall in said housingbetween said photosensitive element and said lens having an elongatedhorizontally disposed aperture therein located at the focal plane ofsaid lens, said aper ture limiting the light falling on saidphotosensitive element to that approaching said opening from withinpredetermined vertical and horizontal angles, and a light refractingelement in said housing and adjacent said aperture to substantiallyequalize the actuating efiect on said photosensitive element of thelight entering said opening irrespective of its angle of approach withinsaid predetermined angles, and mounting means on said unit adapted tosecure said unit to a vehicle.

13. A light pickup unit for a vehicle automatic headlight dimmer devicecomprising a housing having an opening therein, an electron multiplierphotosensitive element in said housing, a condensing lens element insaid opening, an opaque wall in said housing between said photosensitiveelement and said lens having an aperture therein located at the focalplane of said lens, said aperture limiting the light falling on saidphotosensitive element to that approaching said opening from withinpredetermined vertical and horizontal angles, a light refracting elementin said housing and adjacent said aperture to substantially equalize theactuating effect on said photosensitive element of the light enteringsaid opening irrespective of its angle of approach within saidpredetermined angles, light filter means in said housing to block bluelight from said electric multiplier photosensitive element, and mountingmeans on said unit adapted to secure said unit to a vehicle.

14. A light pickup unit for a vehicle automatic headlight dimmer deviceas set forth in claim 13 and wherein at least one of said condensinglens element and said light retracting element contains the light filtermeans.

15. In a vehicle having a windshield, a light pickup unit for anautomatic headlight dimmer device comprising a housing having an openingtherein, a photosensitive element in said housing, a condensing lens insaid opening, an opaque wall in said housing between said photosensitiveelement and said lens having an aperture therein located at the focalplane of said lens, said aperture limitinig the light falling on saidphotosensitive element to that approaching said opening from withinpredetermined vertical and horizontal angles, and optical means in saidhousing and adjacent said aperture to substantially equalize theactuating eifect on said photosensitive element of the light enteringsaid opening irrespective of its angle of approach within saidpredetermined angles, and adjustable mounting means on said unitsecuring said unit to the vehicle behind the windshield thereof so thatthe opening in said housing faces the windshield.

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